Conventionally known methods for producing α-L-aspartyl-L-phenylalanine-α-methyl ester (hereinafter, “α-APM” for short in some cases) include a chemical synthesis method and enzymatic synthesis method. As the chemical synthesis method, there has been known a method for condensing an N-protected L-aspartic acid anhydride with L-phenylalanine methyl ester to synthesize an N-protected APM and eliminating the N-protecting group to obtain APM, and as the enzymatic synthesis method, there has been known a method for condensing an N-protected L-aspartic acid with L-phenylalanine methyl ester to synthesize an N-protected APM and eliminating the N-protecting group to obtain APM. In both of the methods, however, steps of introducing a protecting group and eliminating the protecting group are necessary and the processes are very troublesome. On the other hand, an APM production method in which no N-protecting group is used has been studied (see Japanese Patent Publication No. H02-015196 Gazette). However, this method is not suitable for industrial production due to very low yield of the product. Thus, under such circumstances, development of industrial production methods for aspartame at lower cost has been desired.